1. Field of the Invention
The present invention relates to an apparatus that is installed on automobiles and other vehicles for detecting their passenger occupancy or the physique of passengers.
2. Description of the Related Art
In view of enhancing the safety and comfort of vehicles, it has recently been proposed that the passenger occupancy of vehicles and the physique of passengers are detected and control is performed in accordance with the obtained information. A typical example of this approach is the control of an air bag device that is installed on a vehicle and activated upon crash. The air bag device is required to operate optimally in accordance with the presence or absence of a passenger or the physique of any passenger (e.g. whether the passenger is an adult or a child).
Japanese Patent Unexamined Publication (kokai) No. 169289/1996 describes an apparatus that detects the passenger occupancy of a vehicle and the seating poisture of passengers. The apparatus is composed a seat position sensor that detects the position of a seat relative to the vehicle and which outputs the relevant information about the seat position and a distance sensor that is installed on the vehicle and which detects the distance to the passenger on the seat. The apparatus checks if any passenger rests on the seat on the basis of the acquired seat position information and distance information. The distance sensor projects infrared rays onto a predetermined point on a passenger, receives the reflection from the passenger and measures the distance to the passenger on the basis of the time over which the light travels to and back from the passenger or the deviation in the wavelength of the light or the incident angle of the reflected light.
Japanese Patent Unexamined Publication (kokai) No. 311105/1988 describes a method of detecting driver's sleeping while driving by first taking the image of the driver's face, then detecting the position of his nose from the image data and finally detecting the positions of his eyes. To detect the nose position, the degree of correlation between a preliminarily constructed standard pattern and the acquired image data is checked and the position of an image having a maximum degree of correlation is used as a basis.
The apparatus described in Japanese Patent Unexamined Publication (kokai) No. 169289/1996 relies on the distance sensor to measure a single point on a passenger and, hence, often fails to achieve correct measurement of the single point if there are disturbances and other undesirable effects. In other words, the precision in the measurement of the distance to the passenger is not high. The method described in Japanese patent Unexamined Publication (kokai) No. 311105/1988 is for detecting driver's sleeping while driving and not for detecting the passenger occupancy of a vehicle or the physique of passengers.